It is well known that turfs for sport fields such as for soccer, hockey, cricket, rugby, etc. provide a natural turf grown on a ground or substrate. Natural turfs offer high aesthetical, technical and environmental performances.
However, with the use and with time, as well as with unfavourable weather conditions the natural turf quickly wears and requires expensive maintenance work. Unless a worn natural turf is completely restored the field is unaesthetic, irregular, and potentially dangerous for the users.
An intense activity, which normally concerns a sport field, worsens the turf characteristics after each use without enough time for the turf to recover. In particular, the field looses its planarity, uniformity and resistance of its substrates, affecting the athletic performances and endangering the athletes.
For these reasons, synthetic turfs have been developed in the last years, having artificial grass blades and granular filling material, for example sand or resilient material, which presents better performances and steadiness of grip on the ground. Such artificial turfs can be installed on surfaces made of various material, in particular asphalt, and stabilized inert material.
The synthetic turf, in particular, must have physical characteristics and technologic typical of natural turfs such as: the elasticity of the playground, the bounce back properties of the ball or other sport tool, capacity of absorption of hits, tensile and torsion resistance caused by a shoe, resistance against compression and penetration of external bodies, as well as absorption and drainage capacity relatively to meteorological and environmental events. The granular infill materials used to provide the substrate of the synthetic field have in general a heterogeneous granulometry between about 500 microns to several millimeters.
However, the artificial turfs have some technical drawbacks, among which a considerable superheating of the field in addition to environmental modifications with subsequent discomfort for the users. For avoiding the above described drawbacks combined systems have been proposed of mixed natural and artificial turf (see WO2006/008579).
A valid alternative for overcoming this problem is provided by Italian patent application PI2003A000036 of May 28, 2003. In this document, a synthetic turf is described with an infill material formed by a mix of sand, vegetable powdered material and rubber granules, in a first configuration providing a layer of sand, a layer of rubber granules and a layer of vegetable material, and another configuration where the vegetable material and the rubber are distributed above the layer of sand after that they have been already mixed to each other. With this system, relevant advantages are obtained, reducing remarkably superheating of the turf, owing to the presence of the vegetable material.
In WO2006109110 and WO2007010324 a process is described completely similar to PI2003A000036 to obtain synthetic turfs, which provides the use of vegetable material based on peat and coconut peat as infill material. In particular, the coconut peat comprises both granular and powder parts. The powder part is in a larger quantity than the former and do not exceed 500 micron diameter. This infill material has, however, the drawback of requiring frequent watering, because in the presence of wind, the infill material can be and creating discomfort to the users.
Furthermore, the powder deriving from grinding the coconuts have a high capacity of water retention that, in case of heavy rain, causes flooding of the turf. In particular, while raining the powder parts of the coconut peat follow and plug the drainage holes made of the mat to which the synthetic grass blades are fixed.
In addition, with time the rainwater can cause the powder to compact thus affecting the drainage of the turf and the technical performances thereof.
Such drawbacks are acknowledged in the specification and possible solutions are proposed, such as compacting the powder through mixing, thickening and granulating the powder peat in order to obtain granules that can be used as infill material for synthetic turfs.
However, such operations cause the process to become complex and expensive both for the apparatus necessary for carrying it out and for use of further materials, such as thickening agents.
Furthermore, with time, the granules produced according to the prior art method above described tend to return in the powder form causing the cited drawbacks.